Present invention relates to an apparatus and method for detecting, compensating, and inspecting for offsets and gain differentials among signal distribution paths, phase shifts of sampling clocks supplied to a plurality of A/D converters, and frequency-dependence of the transfer function and phase response of signal paths, applicable to inspection of a magnetic disk or head, using parallel operation of N pieces of A/D converters.
Conventionally, magnetic recording devices have been used as external storage of information processing devices such as workstations. With recent improvements of magnetic material or magnetic heads and enhancements in signal processing technology, especially, magnetic disk apparatus with even denser recording density and operating at a higher frequency for recording is used. It is generally known that magnetic disk apparatus is available at lower price and contributes to faster processing speed and price reduction of information processing devices.
High reliability of recording and reproducing data is required for the magnetic disk apparatus as external storage. A magnetic recording medium such as, typically, a magnetic disk, or a magnetic head for use in the magnetic disk apparatus is commonly inspected by the following method. Run the magnetic disk or magnetic head at an actual operating frequency and record and reproduce test data onto/from the magnetic disk by the magnetic head.
For inspection apparatus for inspecting a magnetic disk or head in this method, a higher frequency at which test data should be recorded and reproduced is required and it is highly required that reproduced test data should be scrutinized or measured in depth and with high precision. To make the inspection apparatus meet both high-speed and high-precision requirements, a method is available in which reproduced test data is converted into digital data by A/D converters and, by processing the digital data, the test data reproducing performances or the magnetic characteristics of the magnetic disk are calculated with high precision. In order to perform inspection using test data for high-frequency performance in this method, it is necessary to use quite a higher frequency as a sampling frequency of the A/D converters. To accomplish this, the following method is taken: by parallel processing with N pieces of A/D converters, each operating at a sampling frequency fADC, an apparent sampling frequency that is as high as N folds is obtained. FIG. 6 illustrates an inspection apparatus of a magnetic disk or head, using four (N=4) A/D converters which perform processing in parallel.
In the inspection apparatus of a magnetic disk or magnetic recording head 100 shown in FIG. 6, a disk rotating device 103 holds and rotates a disk 11 that is a magnetic disk, a writing data generation device 102 generates and outputs test data for use in inspection. Output of the writing data generation device 102 is amplified by a writing amplifier 101. The test data is recorded as follows. Position a R/W head 12 at a test target track on the disk, write the test data onto the disk 11 having magnetic characteristics, while changing the magnetic field of the R/W head 12, based on the output of the writing amplifier 101, and record the test data on the test target track of the revolving disk 11 in a circumferential direction. Data reproduction and decision as to whether the disk is normal are performed as follows. The R/W head 12 detects change of the magnetic field, based on the test data recorded on the revolving disk 11. Signals detected by the head are amplified by a reproduction amplifier 13 and output as signals reproduced from the disk. The reproduced signals are distributed by a reproduced signal distribution circuit 14 to four (N=4) paths to four (N=4) arranged A/D converters 15 to 18 that individually convert the signals into discrete digital values, using respective sampling clock signals output from a sampling clock distribution circuit 19. The discrete digital values output from the A/D converters 15 to 18 are retained in memories 20 to 23. Based on the reproduced signal data as the discrete digital values retained in the memories 20 to 23, a data processing device 27 calculates objective measurements of the reproduced signals by arithmetic operation. Based on the measurements of the reproduced signals output from the data processing device 27, an analytic processing device 28 performs calculation and decides whether the inspected disk is normal. In this way, a magnetic recording medium such as, typically, the magnetic disk 11, or the magnetic head 12 put to inspection is inspected.
The data processing device 27 is constituted by logic circuitry such as, for example, a digital signal processor (DSP) for digital signal processing. Based on the discrete digital values of the reproduced signals retained in the memories 20 to 23, it executes interpolation or the like and computing, thereby calculating pulse amplitude or average pulse amplitude for arbitrary reproduced signal pluses. By computing for frequency analysis of the retained digital values, based on Fast Fourier Transform (FFT) or Discrete Fourier Transform (DFT), it is possible to perform in-depth inspection of the magnetic disk or magnetic head.
By employing four (N=4) A/D converters 15 to 18 for parallel processing in the inspection apparatus configuration, as described above, the signals reproduced from the disk are sampled at closer intervals in the time axis direction. Consequently, for example, a spike in the reproduced signals can be converted into discrete digital values with high precision. By using high-precision discrete digital values data in calculating magnetic disk characteristics by digital computation, high-precision inspection of a magnetic recording medium such as, typically, a magnetic disk, or a magnetic head can be performed.
This example of previous technique for magnetic disk or head inspection is disclosed in Japanese Unexamined Patent Publication 2001-184602.